Serum IGM response, hepatic viability, and survival of tilapia in KPP5 PHAGE-Klebsiella pneumoniae KP001 interaction

Bacterial infections caused by Klebsiella pneumoniae pose a growing threat to aquaculture, particularly in red hybrid tilapia (Oreochromis spp.) farming. This study evaluates the therapeutic potential of K. pneumoniae Phage 5 (KPP5) in enhancing fish survival, controlling K. pneumoniae strain 001 (KP001) burden in the liver, and modulating immunoglobulin M (IgM) levels. Red hybrid tilapia were experimentally challenged with a median lethal dose (LD50) of KP001 and subsequently treated with purified KPP5 at a multiplicity of infection (MOI) of 1.0. The phage-treated group exhibited lesser mortality rate (35%) compared to 60% mortality rate in the untreated infected group, with a relative percentage survival (RPS) of 41.67%. Hepatic analysis revealed complete bacterial clearance in treated fish at all time points, while untreated fish showed high bacterial loads and delayed clearance. Concurrently, hepatic phage titres remained higher in infected fish than in phage-only control, indicating sustained in vivo replication of KPP5 in the presence of its bacterial host. IgM concentrations in serum was markedly elevated in the phage-reated group, suggesting enhanced adaptive immune responses. These findings support the use of KPP5 as a viable and effective alternative to antibiotics, promoting fish survival while contributing to immune resilience and bacterial control in aquaculture settings. Future studies should focus on investigating long-term immune effects.